In its initial report released Tuesday, the NTSB said the battery sustained “severe fire damage.”

“Thermal damage to the surrounding structure and components is confined to the area immediately near the APU battery rack (within about 20 inches) in the aft electronics bay,” NTSB writes.

The NTSB has three investigators looking into the incident. The Federal Aviation Administration, Boeing, Japan Airlines and a representative of the Japan Transport Safety Board also are investigating.

In a statement released Tuesday, Boeing says it would be premature to discuss details. However, the company said it does not think previous incidents involving 787 electrical components are related to this latest one.

“Nothing that we’ve seen in this case indicates a relationship to any previous 787 power system events, which involved power panel faults elsewhere in the aft electrical equipment bay,” Boeing said in an emailed statement.